a) Field of the Invention
The present invention concerns an apparatus for drying hair.
b) Description of Related Art
Hair drying devices including the widely known hand held hair dryer appliance have been in use for many years. The hair dryers which are most commonly used by the consumer differ very little in fundamental design. The known prior art embodiments include a motor driven fan which forces air across or through a resistance heating element as disclosed in U.S. Pat. No. 3,863,651 to Vaiano wherein the drying apparatus is embodied within a system for washing and conditioning hair. Another technique uses refrigeration components to lower the absolute humidity of the air within the evaporator portion of a refrigeration system, then reheats the air within the condenser portion before passing it over the hair as disclosed in U.S. Pat. 2,392,405 to Phipps. Hair drying apparatus have since been simplified, eventually embodying the common hand held "blow dryer" of contemporary times. These hair dryers, which operate by forcing a stream of air over an extremely hot resistance heating element, are crude but effective. They are generally rated by power input (watts) with the average hair dryer in the consumer market being rated at a power input anywhere from 1200 to 1800 watts. This power requirement using 115 volts of alternating current will draw as much as 13-16 amperes of current and will result in an air temperature of 150-200 degrees Fahrenheit. This temperature range is thought to be required to dry hair, however, these temperatures have been known to cause damage to the hair over a period of time; and the extremely high current draw, which is not economical, also represents a potential electrical shock hazard to the user. The low voltage, low current, thermoelectric dryer described herein represents a radical yet sophisticated departure from the prior art hair dryer designs which are common in the contemporary marketplace.
Thermoelectric refrigeration, which is the principle upon which the present invention is embodied, is based on the Peltier effect, a reciprocal of the Seebeck effect, which was discovered early in the nineteenth century. Both effects deal with the interrelationship of heat energy and electrical energy in a circuit which contains a junction of dissimilar metals, primarily bismuth and tellurium sufficiently doped to create an excess or deficiency of electrons. Much research has been done in the field of electrical power generation as a result of the Seebeck effect exhibited by thermoelectric modules. Electric power results by applying heat to one face of the thermoelectric module while keeping the opposite face at a considerably lower constant temperature.
U.S. Pat. No. 3,625,279 to Mayo discloses a thermoelectric module heated by a radioactive isotope heat source thereby generating power to operate a pump for circulating cooling and/or heating fluids in a flight suit.
Several appliances utilizing thermoelectric modules for cooling are available, the most common being a thermoelectric refrigerator. In a known embodiment, heat sinks are placed in thermal communication with each face of the module. One face of the module is placed within an interior insulated space of the refrigerator, and the opposite face is located exteriorly, exposed to ambient conditions. Electric current is applied to the module and a fan inside the refrigerator forces air over the interior heat sink, which by virtue of contact with the module, absorbs the heat within the insulated space. The heat is rejected from the module when another fan forces air over the exterior heat sink surfaces in contact with the opposite face of the module. The interior space can also be heated simply by changing the direction of current flow to the module thereby causing the interior heat sinks to reject heat absorbed from the air on the exterior. A refrigerator of this type is disclosed in U.S. Pat. No. 4,364,234 to Reed, the essence of which is an elaborate electronic technique for maintaining accurate temperature settings.
A thermoelectric device utilized as a fingernail polish drying apparatus is disclosed in U.S. Pat. No. 4,464,906 to Outlaw. As in Reed, the Outlaw device is essentially used to cool air below ambient temperature with the cool air being recirculated within a closed loop inside a confined space.
Another use of a thermoelectric cooling module is disclosed in U.S. Pat. No. 5,139,347 to Apisdorf, wherein ambient air is forced across the cold face of a module at low velocity and directed toward the face of a helmeted worker in a hot environment, for the purpose of cooling the face of the worker. The heat absorbed from the cool side of the module is rejected at the hot side through a heat sink by natural convection, thereby differing slightly from the aforementioned embodiments. It is important to note in the Apisdorf disclosure that the air must be moving across the cold face of the thermoelectric module at a low velocity in order to obtain the desired cooling effect. In fact, if air is moved at a high velocity, no measurable cooling can be obtained, and no purpose would be served by embodying the module.
U.S. Pat. No. 5,282,364 to Cech also discloses the common structure of a thermoelectric cooling module "sandwiched" between heat sinks. In the Cech disclosure, more focus is directed toward the efficient transfer of heat by use of multiple extrusions forming fins, and once again a fan on the inside of a refrigerator forces air over the interior fins and a fan on the exterior of the refrigerator forces air over the exterior fins.
In all of the aforementioned disclosures, the common component is the thermoelectric module, however, none of these prior art embodiments address the possibility of constant operation at the highest heat pumping capacity of the module.
In the field of thermoelectrics it is widely known that as heat is removed from a confined space, the heat pumping capacity of the module diminishes. This is simply because the interior space being insulated from the ambient has less heat available for the module to remove. Unless the module is cascaded in stages with another module, the lowest temperature which may be obtained in the confined area for all practical purposes is approximately 40 degrees Fahrenheit. At this temperature the module is moving very little, if any, heat. Stated differently, the greater the temperature difference between the hot and cold faces of the module, the less heat pumping capacity is present and consequently the coefficient of performance is lowered proportionately.
A limitation on heating is built into the module as well, because of the materials of which it is constructed. Any heat, including joules heat, produced by the input power to the module, must be rejected rapidly or it will build up and cause the device to stop functioning. There exists the possibility of overheating and melting the low temperature solder which holds the module together. This concern is most prevalent when the module is used for heating or cooling a confined space.
In the present invention described herein, the thermoelectric module is constantly operated at its highest heat pumping capacity, and coincidentally its highest coefficient of performance. This condition is known as DT=0, or zero temperature differential. During this condition, which normally exists for only a very short period of time in any other thermoelectric cooling or heating mode, the module possess the capability of constantly pumping a quantity of heat greater than its normal design capacity, the equation being Q.sub.h =P.sub.in +Q.sub.c where Q.sub.h is the heat rejected by the module in watts, P.sub.in is the input power, and Q.sub.c is the heat absorbed by the cold face of the thermoelectric device. Stated differently, the performance of the thermoelectric module is boosted to a higher level without concern for adverse effects. Operated at this performance level, for the purpose of heating, the thermoelectric module is well suited for use in a hair dryer, and because the heat which is produced is constantly being discharged to ambient air at high velocity, there is no possibility of heat build-up in the module as in conventional heating uses of the module. The cold side of the module being exposed to the same high velocity airstream supplies the module with substantial amounts of both sensible and latent heat. The air, after having been exposed to the cold face of the module is also discharged to ambient conditions and/or can be mixed with the air which has been exposed to the hot face, thereby providing a unique and simplified method of air temperature adjustment which does not rely on electronic controls. The thermoelectric hair dryer consumes very little power compared to conventional hair dryers and provides a new and unique application for the Peltier effect thermoelectric module.